gertty: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On Debian possible default full paths are:

/usr/bin/gertty - from package: gertty

You may install the required package with command apt-get install {package}

Error in other languages:
gertty: bevel nie gevind nie
gertty: comandă negăsită
gertty: comando não encontrado
gertty: commande introuvable
gertty: command not found
gertty: käsku ei ole
gertty: không tìm thấy lệnh
gertty: komanda nerasta
gertty: Kommando nicht gefunden.
gertty: kommandot finns inte
gertty: komut yok
gertty: nie znaleziono polecenia
gertty: níor aimsíodh an t-ordú
gertty: no se encontró la orden
gertty: no s'ha trobat l'ordre
gertty: opdracht niet gevonden
gertty: parancs nem található
gertty: perintah tidak ditemukan
gertty: príkaz nenájdený
gertty: příkaz nenalezen
gertty: команда не найдена
gertty: командата не е открита
gertty: 命令找不到
gertty: コマンドが見つかりません